Tires for vehicles are formed from rubber compositions containing natural rubber and/or synthetic diene rubbers as raw materials. Such tires deteriorate in the presence of ozone and may then be cracked. In order to suppress crack formation and growth in the presence of ozone, for example, additives such as an antioxidant (e.g. N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine (6PPD), poly(2,2,4-trimethyl-1,2)dihydroquinoline (TMDQ)) or petroleum wax are added to rubber compositions.
The antioxidants and petroleum wax in vulcanized rubber migrate (bloom) to the surface of rubber such as tires, thereby protecting the rubber from ozone. However, excessive blooming of the antioxidants and petroleum wax in a short time causes white discoloration. Moreover, the antioxidants degraded by ozone cause brown discoloration, and similar excessive blooming of them intensifies brown discoloration. In addition, if the wax and the like bloomed on the tire surface form irregularities, diffused reflection of light occurs, making the brown discoloration caused by the degraded antioxidants more noticeable. Thus, the shine of the tires is also lost.
Patent Literature 1 discloses that addition of a polyoxyethylene ether nonionic surfactant prevents deterioration of tire appearance. However, there is room for improvement in discoloration resistance and tire appearance while maintaining good handling stability, crack resistance, and ozone resistance or improving these properties.